1. Field of the Invention
The invention generally relates to projecting an image onto a surface that is substantially parallel to an axis of light passing through an objective lens, and more particularly to projecting an image from an image representation onto a surface where the angle from one portion of the image representation to the surface is different than the angle from at least one other portion of the image representation.
2. Description of Related Art
A typical image projector will shine a light source towards an image representation, such as a slide or transparency. The light then passes through an objective lens that will magnify the image representation to display an image on a surface.
A well-known image projector currently available is a slide projector. An optical path for a typical slide projector is shown in FIG. 1.
Normally, a slide projector comprises a light source 101 that projects light towards a slide 109 that includes a representation of an image. The light source 101 may have a reflective mirror (not shown) to reflect scattered light back towards the slide, and a lens 105 may be interposed between the light source 101 and the slide 109 to further concentrate light onto the slide. While a condenser lens is shown, a no-sphere (planoconvex) lens could also be used for this purpose. The light beam then passes through a projection/objective lens 115 that magnifies the image and projects it for display onto a surface 120, like a screen or wall. A field lens (not shown) could also be provided that further focuses the entire light beam passing through the slide 109 onto the objective lens 115. The light source 101, slide 105, and objective lens 115 are aligned along a common axis of light. This axis is substantially perpendicular to the surface 120 onto which the image is projected.
Another type of well-known projector is an overhead projector (not shown). Generally, the transparency is substantially perpendicular to the projected image. The light source will shine up through an image representation, which is normally referred to as a transparency, to a housing containing the lenses for projecting the image. The overhead lens housing will include some kind of condenser lens, normally a fresnel lens, to collect light shined through the transparency and direct it to a pupil of an objective lens. The objective lens then projects the image much in the same way as the objective lens in the slide projector. A mirror is then used to redirect the image projected from the objective lens so that the final projected image can be displayed on the surface, which is substantially perpendicular to the transparency. But like a slide projector, the plane of the surface is substantially perpendicular to the direction of light projecting the image from the overhead projector.
In both the slide projector and the overhead projector, the projected image can be easily focused because the distance from the objective lens to the surface is substantially similar for the entire projected image. Therefore, the entire projected image can be at a substantially similar distance from a focal point of the objective lens.
The arrangement of either the slide projector or the overhead projector, however, would not be suitable for projecting an image onto a surface that is substantially parallel to the direction of light projected to display an image. Some portions of the projected image would be much closer to the objective lens, while other portions would be much further from the objective lens. This would distort the image so that the image projection portions closer to the objective lens would appear shortened, and the portions further from the objective lens would appear elongated. As a result, the projectors described above would display the image on a substantially parallel surface with a “fun-house” mirror like effect.
To properly display an image on the substantially parallel surface, a display device like an image projector must account for the varying distances throughout the image projection from the projection/objective lens.